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Lathe DRO mounting question

bikemutt

Aluminum
Joined
Mar 5, 2022
I'm planning to install an optical scale DRO sensor to the cross-slide of a lathe, is there a rule of thumb when deciding whether to attach the scale (the long part), or the head (the short part) to the lathe's measured moving part, the cross-slide in this case?

I'm inclined to mount the head to the carriage and the scale to the cross-slide. It's easier for me to see which one should go where when the scale is very long compared to the head, as in a carriage travel DRO; with this one the head is 1/3 the length of the scale i.e., it's short.

In any event, my thought is to take the approach which affords the most protection for the device from swarf, minimizes compromising lathe travel and clearance specifications, and interferes the least with the lathe's operational controls.

I still have this feeling I may be missing something more important, which is why I ask.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Every set up I've seen has the reader head mounted to the moving part, scale stays stationary.

Erm, for the cross slide that's the exact opposite to every one I've seen. I've always seen them installed so that the scales move with the cross slide, reader head mounted solidly to the carriage; generally on the tailstock side, but have heard tell of some actually installed inside the cross slide. For longitudinal on the other hand, the scales are generally mounted to the bed casting and the reader head moves with the carriage.
 

RJT

Titanium
Joined
Aug 24, 2006
Location
greensboro,northcarolina
A cover over the whole thing is your best insurance. Mount the scale / reader head with the open side of the scale on the bottom to help keep things clean .
 

tylersteez

Aluminum
Joined
Jul 9, 2019
Erm, for the cross slide that's the exact opposite to every one I've seen. I've always seen them installed so that the scales move with the cross slide, reader head mounted solidly to the carriage; generally on the tailstock side, but have heard tell of some actually installed inside the cross slide. For longitudinal on the other hand, the scales are generally mounted to the bed casting and the reader head moves with the carriage.
Yeah I wrote that while having a complete brain fart, disregard it entirely:crazy:
 

bikemutt

Aluminum
Joined
Mar 5, 2022
Alright then, I'll proceed with mounting the scale to the cross-slide and the head to the carriage.

Appreciate the help!
 

bikemutt

Aluminum
Joined
Mar 5, 2022
PLAN ON... also adding some sort of stand-off post or "bumper", not 'just' a cover.

MOST lathes, some portion of the TS can come right up to touch the saddle under the cross.
Not a surprise, is that?

And .. with not enough 'for sure' clear space for the DRO's works.
Not welcome if a surprise, is that?.

I had to really think about this for a while, then I got it. If nothing else, I know better than to be deaf to good advice.

In this case, I'm installing on the chuck side of the cross-slide. I give up a very small amount of swing to bed, and even less of useful travel. When I clamped things up on the TS side, it got messy. I've got tapped holes on both sides of the slide so I can punt and swap if the need arises.
 

ballen

Titanium
Joined
Sep 25, 2011
Location
Garbsen, Germany
If you use a low-profile scale (16 x 19mm) you might even be able to mount it inside the cross slide:

All else being equal, let the scale move so that the read head is fixed. That way you can tie down the cables in a fixed position where they are protected.
 

car2

Stainless
Joined
Sep 19, 2009
Location
Apex, NC
And strain-relieve the cables so they don't bend and tug at the readhead. I made a delrin u-bracket that screws to the end of the scale housing to support the readhead cable (mine are metal-clad) when it's moving around, and keeps it from getting pinched or caught by the cross-slide and carriage moving around,.
 

bikemutt

Aluminum
Joined
Mar 5, 2022
Just for completeness, thermite and eKretz were right; mounting the scale on the spindle side of the cross-slide was not a good place, it became a swarf magnet 😒.

I moved it to the tailstock side, the world is a better place, lol.

Thanks, you guys are awesome!
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Also, don't forget you now have a "zero" for your tailstock if doing repetitive parts. (As long as you have tool offsets available). On the first part, lock down the t'stock, set up your drill so that it's at a reference point in relation to the part (just cut in to full depth or just touching the part, for example) then run the carriage back to just touch the front of the tailstock and punch 'Z' axis zero. From there you can drill, chamfer or whatever to the same depth every time by using the tailstock graduations.

Next part, you set the carriage at 'Z' zero first, then lightly bump the t'stock up to it and lock it down. Alternatively you can set the carriage closer to the chuck, leave the t'stock loose but bumped to the carriage and use the carriage to push the t'stock back to 'Z' zero before locking it down.
 








 
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